Use in medical technology offers particular advantages, where frequently, in particular in the case of minimally invasive medical procedures, movements via shafts, in particular flexible shafts, must be transmitted through small openings or vessels occurring naturally in the body under particularly difficult surrounding conditions.
A particular type of application is represented by the actuation of liquid pumps in microconstruction, which are applied for example as heart pumps and which can be brought with a heart catheter to the operating place thereof, for example a ventricle.
For this purpose, not only do the corresponding pumps require to have a very small constructional size but also difficult conditions are present for the transmission of the pump power via a shaft. The shaft normally extends through a heart catheter and is actuated from outside the body through a leadthrough. At the distal end of the catheter, the movement is transmitted to the pump. Such shafts are usually flexible so that intensive deformations take place in particular in the case of the high speeds of rotation which are required. Therefore, not only are particularly high requirements placed upon achieving high speeds of rotation but also upon dissipating the corresponding heat which is produced by the deformation of the shaft.
A corresponding heart catheter is normally filled with a liquid which is tolerated by the body in order to lubricate the shaft, on the one hand, and to cool it, on the other hand.
Since corresponding shafts are normally composed and twisted from thinner strands in order to promote their flexibility, a spindle-shaped surface structure is produced, which, during rapid rotation, leads to conveyance of the fluid situated in the catheter along the shaft. This effect is generally undesired since it produces a pressure drop in the fluid in the catheter. From the drive-side end of the catheter, new fluid must flow along. If this is not available, then, either through the shaft leadthrough or also through a ventilation opening which can be provided likewise in the region of the catheter close to the drive and which serves for ventilating the catheter, undesired liquids or gases, for example air, can be suctioned in.
Normally, a supply line for the fluid situated in the catheter is provided, through which the fluid is pumped along by means of a pump device. It is thereby advantageous to pump a quantity of fluid which is not too large, i.e. to produce a very small volume flow. If however the pump of the fluid supply line does not provide an adequate volume flow, then a low pressure which is undesired is produced in the region of the fluid inflow as a result of the suction tendency of the shaft.